alsabat: add terminate status check for capture thread

alsabat: add terminate status check for capture thread

In loopback test, alsabat use pthread_join(pthread_t thread, **retval)
to wait for the capture thread to terminate. If the capture thread was
canceled, PTHREAD_CANCELED is placed in *retval, and the access to the
**retval will fail. Add status check to prevent illegal access to the
**retval.

Signed-off-by: Lu, Han <han.lu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>